This invention relates generally to medical imaging systems, and more particularly, to methods and systems for calibrating a Computed Tomography (CT) system.
An increase in the precision of medical imaging and diagnosis has led to a need for even more precise calibration and alignment of medical imaging systems. For example, Radiation Therapy (RT) for oncology patients requires the patients to be positioned accurately on a CT scanner table and that the resulting CT images be rendered with good positional accuracy. In a CT system, lasers are used for accurate positional registration. Misalignment of lasers may affect the correct positioning of the patient on the table. This misalignment may affect the planning of treatments that require good positional accuracy in the reconstructed CT images. For example, in Radiation Therapy (RT) systems, even a small rotation of half a degree in the image is undesirable as it may have a significant effect on the treatment of a patient.
In a CT system, the rotational misalignment may be attributed to errors in the mechanical setup. Examples of errors in the mechanical setup include, but are not limited to, unleveled stationary base of the CT system, incorrect angular position of encoders on the gantry of the CT system, inaccuracy of the encoder pulse with respect to the encoder gear tooth, and the like. These inaccuracies result in the rotation of the final image with respect to the actual positioning of the object being scanned. These inaccuracies also result in the rotation of the positioning lasers.
Existing methods address these problems either on an ad-hoc basis or do not provide a robust solution.